1. Field
Aspects relate to an apparatus and method to control the temperature of a heating roller used in a fusing device of an image forming apparatus.
2. Description of the Related Art
In order to perform printing at high speed, an induction heating fusing device that heats a surface of a heating roller at high speed is often used in an image forming apparatus. The induction heating fusing device is categorized as an internal coil type fusing device in which a ferrite core and an induction coil for heating the heating roller are located inside the heating roller or as an external coil type fusing device in which an inductor composed of an induction coil and a ferrite core is located outside the heating roller. The internal coil type fusing device has problems in that it takes lots of time for heat output from a heating element inside the heating roller to reach the surface of the heating roller and when the heating roller needs to be replaced, both the ferrite core and the induction coil, which are generally expensive, should be replaced. Accordingly, in order to solve the problems mentioned above, the external coil type fusing device is used. The external coil type fusing device is configured in such a way that the induction coil is wound in a horseshoe-like shape at both ends of the heating roller. In this configuration, however, the heating performance at both ends of the heating roller is drastically reduced due to a change in an electromagnetic field in both ends of the heating roller. Accordingly, the external coil type fusing device has problems in that, in order to increase the heating performance, the heating roller should be lengthened, thereby increasing the size of the image forming apparatus, and when sheets of paper having a size that is less than the size of the heating roller, such as B5 size paper, are continuously printed, the temperature of an unused area of the heating roller on which paper is not passed is increased. Accordingly, there is a demand for a method of preventing the temperature of an unused area of a heating roller from increasing even when paper having a small size is printed, without increasing the size of the heating roller.